Electroplated copper

ABSTRACT

An electroplated copper metal having certain grain misorientations between adjacent grains at a &lt;111&gt; crystal plane direction provides for improved properties of the copper. A method of electroplating the copper metal on substrates, including dielectric substrates, is also disclosed.

Field OF THE INVENTION

The present invention is directed to electroplated copper and methods ofelectroplating the copper where copper metal has high tensile strength.More specifically, the present invention is directed to electroplatedcopper and methods of electroplating the copper where copper metal hashigh tensile strength and has a certain percentage of specific anglemisorientations between adjacent grains of the copper metal with respectto a crystal plane direction of <111> to provide the high tensilestrength copper metal in addition to other improved material properties.

BACKGROUND OF THE INVENTION

In the drive toward future applications in the electronics industry,such as artificial intelligence and autonomous vehicles, advancedsemiconductor packaging products and processes that enable high densitycircuits, reduced form factor (size, configuration or physicalarrangement of a device) and increased functionality in electronicdevices are highly desired. In addition to the required smaller packagesize, more reliable chip-to-chip, chip-to-circuit board, and terminal toterminal interconnects are increasingly in demand. For example, copperhas been used for interconnect applications for the past few decades,such as in copper redistribution Layers (RDL) which are used to rerouteconduction paths within chip packages. As the package size decreases,the demand for reliable fine-line RDLs is increasing. During thermalcycling tests (TCT) copper cracking has been reported for fine-line RDLsdue to thermal stresses induced from the differences in the coefficientof thermal expansion (CTE) of copper and adjacent materials when cyclingbetween hot and cold chambers. The pathway to resolve the cracking issueis still controversial. In conventional printed circuit board (PCB)applications, high elongation copper is commonly known as the preferredway to resolve the cracking issue. However, as feature sizes ofelectronic components on PCBs decrease and the components become moreintegrated to microsized and even to nanosized dimensions, such as iscurrently taking place in advanced packaging applications, this approachmay not be suitable. There is another school of thought which arguesthat high material strength or high tensile strength, not highelongation, is essential to avoid copper cracking upon multiple thermalcyclings. A disadvantage of copper with high tensile strength is thatsuch copper can become brittle. One approach to addressing the problemof cracking is to use nanotwinned copper which is characterized byhaving both high tensile strength and high elongation. Althoughnanotwinned copper may be suitable to address the problem of cracking ofcopper in RDLs, nanotwinned copper has been found to be unsuitable inmany applications for plating vias, such as in advanced packagingapplications where 3D stacking is needed to increase circuit densities.In many such applications via fill has not been found to be acceptableand the surface of the copper deposits have been found to beunacceptably rough and nonuniform.

Therefore, there is a need for a copper metal which can withstandthermal stresses induced from differences in the CTE between copper andadjacent materials when cycling between hot and cold chambers withoutthe copper cracking and enables smooth and uniform copper deposits infeatures, even in high circuit density application.

SUMMARY OF THE INVENTION

The present invention is directed to a copper metal including twinfractions of 30% or greater of grain boundaries between adjacent coppergrains having angles of misorientation of 55° to 65° with respect to acrystal plane direction of <111>.

The present invention is also directed to a method of electroplatingcopper including:

-   -   a) providing a substrate;    -   b) providing a copper electroplating bath comprising one or more        sources of copper ions to provide the copper ions at        concentrations of 20 g/L to 55 g/L, one or more reaction        products of one or more imidazole compounds, or one or more        2-aminopyridine compounds with one or more bisepoxides, wherein        the one or more reaction products are at concentrations of 2 ppm        to 15 ppm; an electrolyte; one or more accelerators, wherein the        one or more accelerators are at concentrations of 0.5 ppm to 100        ppm; and one or more suppressors, wherein the one or more        suppressors are at concentrations of 0.5 g/L to 10 g/L;    -   c) immersing the substrate in the copper electroplating bath;    -   d) electroplating copper on the substrate to deposit a copper        layer on the substrate; and,    -   e) heating the copper layer to a temperature of at least 200        ° C. in an inert atmosphere to provide a copper layer comprising        twin fractions of 30% or greater of grain boundaries between        adjacent copper grains having angles of misorientation of 55° to        65° with respect to a crystal plane direction of <111>.

The copper metal of the present invention has improved tensile strengthover many conventional copper metals deposited from copper plating bathsor by physical or chemical vapor deposition. In addition, the coppermetal of the present invention has good elongation and low thermalstress. The properties of the copper metal of the present inventioninhibit the copper metal from cracking when the copper metal is exposedto heat in high temperature environments, such as TCT and as are foundin annealing processes. The copper metal electroplating compositions ofthe present invention can be used to electroplate the copper metal ofthe present invention at high current density applications withnon-conformal plating where the copper is simultaneously deposited on asurface of a substrate at a faster rate than in apertures, such as vias,within the substrate to provide smooth and uniform copper deposits inthe aperture and on the surface of the substrate. The method of thepresent invention can also electroplate the copper metal of the presentinvention directly on or adjacent to metal seed layers which areadjacent to or joined to dielectric or semiconductor materials used inelectronic devices where the CTE of the materials differ without theconcern for cracking. The copper metal of the present invention ishighly suitable for fine line redistribution layer technology used inadvanced packaging where redistribution line pitch is decreasing andcircuit density is increasing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an inverse pole figure of copper metal of the presentinvention showing grain boundaries and grain boundary angles withrespect to a crystal plane direction of <111>, and the differentorientations;

FIG. 2 is an inverse pole figure of a comparative copper metal showinggrain boundaries and grain boundary angles with respect to a crystalplane direction of <111>, and the different orientations; and

FIG. 3 is an X-ray diffraction graph of diffraction intensity (I) vs.diffraction angle of 2θ (°) of area of copper metal of the presentinvention vs. area of a comparative copper at crystal plane (111) vs. atcrystal plane (200) according to Jade 2010 MDI software application fordata analysis.

DETAILED DESCRIPTION OF THE INVENTION

As used throughout this specification the following abbreviations shallhave the following meanings unless the context clearly indicatesotherwise: A=amperes; A/dm²=amperes per square decimeter=ASD; DC=directcurrent; ° C.=degrees Centigrade; mmol=millimoles; mg=milligrams;g=gram; L=liter; mL=milliliter; ppm=parts per million=mg/L; m=meters; μm=micron=micrometer=10⁻⁶ meters; mm=millimeters; cm=centimeters;nm=nanometers=10⁻⁹ meters; Å=angstroms=1×10⁻¹⁰ meters; 2.54 cm=inch;MPa=megapascal=N/m²; N=Newtons; kV=kilovolts; V=volts=joule/coulomb;mA=milliamperes; DI=deionized; mJ=millijoules; Joule=kg(m)/s²;kg=kilograms; s=seconds; Mw=weight average molecular weight; Mn=numberaverage molecular weight; wt %=weight percent; XRD=X-ray diffraction;EBSD=electron backscatter diffraction; FE-SEM=field emission scanningelectron microscope; EO/PO=ethylene oxide/propylene oxide copolymer;IPF=inverse pole figure; RDL=redistribution layer; N₂=nitrogen gas;vs.=versus; e.g.=example; ohm-cm resistance; and L/S=line spacing ordistance between two features or structures, such as for an RDL.

As used throughout this specification, the term “plating” refers tometal electroplating. “Deposition” and “plating” are usedinterchangeably throughout this specification. The terms “composition”and “bath” are used interchangeably throughout the specification.“Accelerator” refers to an organic additive that increases the platingrate of the electroplating composition and is also used to improvebrightness of copper deposits. “Suppressor” refers to an organicadditive that suppresses the plating rate of copper duringelectroplating. The term “electrolyte” means a chemical compound whichdissociates into ions and hence capable of transporting electric charge,e.g. an acid. The term “moiety” means a part of a molecule or polymerthat may include either whole functional groups or parts of functionalgroups as substructures. The terms “moiety” and “group” are usedinterchangeably throughout the specification. The term “aperture” meansopening, hole, gap or via. The term “aspect ratio” means thickness ofthe substrate divided by the diameter of the aperture of a feature inthe substrate. The term “grain boundary” means the interface between twograins, or crystallites, in copper metal, wherein grain boundaries are 2dimensional defects (2D) in the crystal structure of the copper. Theterm “grain”, “crystal” and “crystallite” are used interchangeablythroughout this specification. The term “misorientation” means thedifference in crystallographic orientation between two grains, orcrystallites, with a common interface, wherein crystallographicorientation between the two grains, or crystallites, can range from0-180° angles, wherein 0° indicates a perfect crystal without anymisorientations. The term “tensile strength” means the resistance of amaterial to breaking under tension. The term “thermal stress” meansstress that occurs as a result of thermal expansion of copper structuralmembers when its temperature changes. The term “annealing” means a heattreatment that alters the physical and sometimes chemical properties ofa material. The term “Miller Indices: (hkl), [hkl], {hkl} and <hkl>”mean the orientation of a surface of a crystal plane defined byconsidering how the plane (or any parallel plane) intersects the maincrystallographic axis of a solid (i.e., the reference coordinates—x, y,and z axis as defined in a crystal, wherein x=h, y=k and z=I), wherein aset of numbers (hkl), [hkl], {hkl} and <hkl> quantify the intercepts andare used to identify the plane. The expression “(hkl)” defines aspecific crystal plane in a lattice. The expression “[hkl]” defines thespecific direction of a crystal plane in a lattice. The expression“{hkl}” defines the set of all planes that are equivalent to (hkl) bythe symmetry of the lattice. The expression “<hkl>” defines the set ofall directions that are equivalent to [hkl] by the symmetry of thelattice. The term “plane” means a two-dimensional surface (having lengthand width) where a straight line joining any two points in the planewould wholly lie. The term “lattice” means an arrangement in space ofisolated points in a regular pattern, showing the position of atoms,molecules or ions in a structure of a crystal. The term “grain boundaryenergy” means the energy at an interface between two grains due tointerface formation. The term “crystallographic domains” means atomsinside a specific space have the same atomic arrangements,crystallinity, orientations and symmetry. The term “texture(crystalline)” means distribution of crystallographic orientations of acopper sample, wherein the sample in which these orientations are fullyrandom is said to have no distinct texture and, if the crystallographicorientations are not random, but have some preferred orientation, thenthe sample has a weak, moderate or strong texture, wherein the degree isdependent on the percentage of crystals having the preferredorientation. The term “slip system” means a set of symmetricallyidentical slip planes and associated family of slip directions for whichdislocation motion can easily occur and lead to plastic deformation,wherein an external force makes parts of the crystal lattice glide alongeach other, changing the material's geometry. The term “pitch” means afrequency of feature positions from each other on a substrate. The term“amino group”=—NHR, where R is —H (hydrogen) or a linear or branchedhydrocarbyl group. The term “aminoalkyl”=-(C₁-C₄)—NH—R, where R—H(hydrogen) or a linear or branched hydrocarbyl group. The term“hydrocarbyl group” means a hydrogen and carbon functional group. Theterm “halide” means chloride, fluoride, bromide and iodide. The term“adjacent” means directly on or next to such that two structures ormaterials have a common interface. The articles “a” and “an” refer tothe singular and the plural.

As used throughout the specification the average of a parameter meansthe sum of the individual measurements of a parameter divided by thenumber of measurements taken for the parameter. Grain size (sphericalequivalent diameter) is based on the calculation that all grains arespherical, wherein grain size area=π(d/2)², wherein d=grain diameter.Copper has a cubic structure of six sides and is the same in alldirections through symmetry. Twin fractions by grain length (μm), andtexture (crystalline) are based on EBSD analysis techniques which issynonymous With FE-SEM. As used throughout the specification themechanical pull test parameters are based on test procedure IPC-TM-650available from IPC® Association Connecting Electronics Industries usingan INSTRON™ pull tester. As used throughout the specification the areaunder the curves ratio of diffraction peak (111) plane orientation anddiffraction peak (200) plane orientation is based on XRD analysis ofdiffraction intensity (I) vs. diffraction angle 2θ (°) as done by Jade2010 MDI software available from KSA Analytical Systems, Aubrey, Tex.

All numerical ranges are inclusive and combinable in any order, exceptwhere it is clear such numerical ranges are constrained to add up to100%.

The present invention is directed to copper metal including twinfractions of 30% or greater of grain boundaries between adjacent coppergrains having angles of misorientation of 55° to 65° with respect to acrystal plane direction axis of <111>. Twin fraction is defined as theratio of the sum of the lengths of grain boundaries in μm withmisorientations of 55° to 65° divided by the sum of the lengths of allgrain boundaries in pm with misorientations of 0° to 1.80° with respectto a crystal plane direction of <111> observed for a given measureablesample area, such as, for example, 60 μm×3 μm.

Preferably, the twin fractions are 35% or greater of grain boundariesbetween adjacent copper grains having angles of misorientation of 55° to65° with respect to a crystal plane direction of <111>; more preferably,the twin fractions are 35% to 55% of grain boundaries between adjacentcopper grains having angles of misorientation of 55° to 65° with respectto a crystal plane direction of <111>; further preferably, the twinfractions are 35% to 52% (e.g. 35%, 37% or 52%) of grain boundariesbetween adjacent copper grains having angles of misorientation of 55° to65° with respect to a crystal plane direction of <111>. Preferably, thegrain boundaries between adjacent copper grains have angles ofmisorientation of 60° with respect to a crystal plane direction of<111>. Such angles of misorientation are thermodynamically stable suchthat the misorientations do not change over time.

The grain boundaries between adjacent copper grains having angles ofmisorientation of 55° to 65° with respect to a crystal plane directionof <111> are high-angle grain boundaries, wherein high-angle grainboundaries are defined as misorientations of angles greater than 10°with respect to a crystal plane direction of <111>. Low angle grainboundaries have misorientations from 2-10° with respect to a crystalplane direction of <111>. In addition to the high-angle grain boundarymisorientations of 55° to 65° with respect to a crystal plane directionof <111>, the copper metal of the present invention can include twinfractions of less than 30% of grain boundaries between adjacent coppergrains having angles of misorientation of less than 55° and greater than65° with respect to a crystal plane direction of <111>. Such angles ofmisorientation can range from 0° to less than 55° and greater than 65°to 180° with respect to a crystal plane direction of <111>.

The copper metal of the present invention has a texture index(crystalline), also referred to as multiples of random distribution(MRD), of equal to or greater than 2, preferably, equal to or greaterthan 5 at (111) plane orientation, such as from 5 to 10.5 (e.g. 5.7 to10.2). High (111) texture indicates that the present invention has more(111) planes that are available for slip to occur because the slipsystem in copper includes a slip plane of {111} and a slip direction of<110>({111}<110>) and therefore results in improved mechanicalperformance of tensile strength and elongation. A texture index of Iindicates random orientation of (111) plane and less copper crystals ina sample having (111) plane orientation, thus less slip which results ininferior mechanical performance of tensile strength and elongation. Atexture index greater than 1 indicates that there are more crystals in asample having (111) plane orientation. Accordingly, a texture index of 2means the number of crystals in a sample with (111) plane orientation is2x more than in a sample having a texture index of 1, and a textureindex of 5 means the number of crystals with (111) plane orientation ina sample is 5× the number of crystal in a sample with a texture index of1 enabling improved slip and improved mechanical properties. Additionalorientations detected at MRD greater than 2 are, for example, (001),(101), (201), (212), (311) and (511), but can have a texture index, suchas less than 5, or such as from 0-5, or such as 1-4 (e.g. 1 to 3.5).

The copper metal of the present invention has an XRD area ratio of (111)plane orientation/(200) plane orientation at diffraction angle 2θ (°)which is equal to or greater than 1 on a graph of diffraction intensity(I) vs. diffraction angle 2θ (°). Preferably, the XRD area ratio of(111) plane orientation/(200) plane orientation at the diffraction angle2θ (°) is greater than or equal to 5. More preferably, the XRD arearatio of (111) plane orientation/(200) plane orientation at thediffraction angle 2θ (⁰) is 5-31 (e.g. 5.3, 21 or 31) which indicatescopper crystals having a high number of (111) planes.

Average grain size (spherical equivalent diameter) of the copper metalof the present invention does not substantially increase upon exposureto heat at high temperatures of 200° C. and greater, such as are foundin annealing processes, thus reducing the potential of cracking of thecopper metal. For example, the average grain size (spherical equivalentdiameter) of all the grains in a copper sample having angles ofmisorientation of 55° to 65° at a crystal plane direction of <111> canbe from 100 nm and greater, preferably, from 500 nm and greater, morepreferably from 1-2 μm before annealing. The average diameter of coppergrains having angles of misorientation of 55° to 65° at a crystal planedirection of <111> have a diameter (spherical equivalent diameter) of100 nm or greater after thermal annealing, preferably 500 nm or greater.More preferably, the average diameter of copper grains having angles ofmisorientation of 55° to 65° at a crystal plane direction of <111> havea diameter (spherical equivalent diameter) of 0.1 μm to 3μm (e.g. 1 μmto 2.5 μm, or such as from 1.4 μm to 2.3 μm) after thermal annealing;even more preferably, the average diameter of copper grains havingangles of misorientation of 55° to 65° at a crystal plane direction of<111> have a diameter (spherical equivalent diameter) of 1 μm to 2.5 μm,most preferably, from 1.5-2.3 μm after thermal annealing. Small grainsize diameter (spherical equivalent diameter) of the copper metal of thepresent invention can strengthen the materials such that the tensilestrength is improved as evidenced by the Hall-Petch relationship: σ_(y)(yield stress)=σ₀+k₁D^(−1/2)

where σ_(y) is the material strength at yield in MPa.

-   -   σ₀ is the material constant for the starting stress for        dislocation movement which is 25 MPa for copper.    -   k₁ is the strengthening coefficient (a constant specific to each        material) which is 0.11 MPa m^(1/2) for copper.    -   D is the average grain diameter in meters.

The copper metal of the present invention is electroplated from aqueousacid copper electroplating compositions (baths) of the presentinvention. The aqueous acid copper electroplating compositions (baths)of the present invention contain (preferably consisting of) a source ofcopper ions and counter anions; an electrolyte; a leveler including(preferably consisting of) a reaction product of one or more imidazolecompounds, or one or more 2-aminopyridine compounds with one or morebisepoxides; an accelerator; a suppressor;

optionally, but preferably, a source of halide ions; and water.

Preferably, the imidazole compounds have the following general formula:

where R₁, R₂ and R₃ are independently chosen from a hydrogen atom,linear or branched (C₁-C₁₀) alkyl, hydroxyl, linear or branched alkoxy,linear or branched hydroxy(C₁-C₁₀)alkyl, linear or branchedalkoxy(C₁-C₁₀)alkyl, linear or branched, carboxy(C₁-C₁₀)alkyl, linear orbranched amino(C₁-C₁₀)alkyl, or substituted or unsubstituted phenylwhere the substituents are chosen from hydroxyl, hydroxy(C₁-C₃)alkyl, or(C₁-C₃)alkyl. Preferably, R₁, R₂ and R₃ are independently chosen from ahydrogen atom; linear or branched (C₁-C₅)alkyl, hydroxyl, linear orbranched hydroxy(C₁-C₅)alkyl, or linear or branched amino(C₁-C₅)alkyl.More preferably R₁, R₂ and R₃ are independently chosen from a hydrogenatom or (C₁-C₃)alky, such as methyl, ethyl or propyl moieties. Examplesof such compounds are 1H-imidazole, 2,5-dimethyl-1H-imidazole and4-phenylimidazole.

2-aminopyridine compounds of the present invention are pyridinecompounds where carbon-2 of the pyridine ring is substituted with anamino group or an aminoalkyl group.

Preferably, 2-aminopyridine compounds of the present invention have aformula:

wherein R₈ is —H or linear of branched (C₁-C₄)alkyl, R₉ is —H, linear orbranched (C₁-C₄)alkyl, halide, linear or branched amino(C₁-C₄)alkyl, orphenyl, and p is an integer of 0-4, wherein when p=0, the nitrogen ofNHRs forms a covalent bond with carbon-2 of the pyridine ring.Preferably, R₈ is —H or (C₁-C₂)alkyl, R₉ is —H of C₁-C₂)alkyl,amino(C₁-C₂)alkyl, chloride and p is an integer of 1-2. More preferably,R₈ is —H or methyl, R₉ is —H or methyl and p is an integer of 1-2. Mostpreferably, R₈ is —H, R₉ is —H and p=2. Exemplary compounds of formula(II) are 2-amino-4-methyl pyridine, 2-amino-5-methyl pyridine,2-amino-5-chloropyridine, 2-aminopyridine, 2-(2-aminoethyl)pyridine and4-(2-aminoethyl)pyridine, wherein 2-(2-aminoethyl)pyridine is preferred.

Preferably, bisepoxides have a formula:

where R₄ and R₅ are independently chosen from hydrogen or (C₁-C₄)alkyl;R₆ and R₇ can be the same of different and are independently chosen fromhydrogen, methyl or hydroxyl; m=1-6 and n=1-20. Preferably, R₄ and R₅are hydrogen. Preferably R₆ and R₇ are independently chosen fromhydrogen, methyl or hydroxyl. More preferably R₆ is hydrogen, and R₇ ishydrogen or hydroxyl. Preferably m=2-4 and n=1-2. More preferably m=3-4and n=1.

Compounds of formula (II) include, but are not limited to,1,4-butanediol diglycidyl ether, ethylene glycol diglycidyl ether,di(ethylene glycol) diglycidyl ether, glycerol diglycidyl ether,neopentyl glycol diglycidyl ether, propylene glycol diglycidyl ether,di(propylene glycol) diglycidyl ether, poly(ethylene glycol) diglycidylether compounds and polypropylene glycol) diglycidyl ether compounds.

The reaction products (levelers) of the present invention can beprepared by various processes known in the art. Typically, one or moreimidazole compounds, or one or more 2-aminopyridine compounds aredissolved in DI water at room temperature followed by dropwise additionof one or more bisepoxide compounds. The temperature of the bath is thenincreased from room temperature to around 100 ° C. Heating with stirringis done for 2-5 hours. The temperature of the heating bath is thenreduced to room temperature with stirring for an additional 8-12 hours.The amounts for each component may vary but, in general, sufficientamount of each reactant is added to provide a product where the molarratio of the moiety from the imidazole compound, or the 2-aminopyridinecompound to the moiety from the bisepoxide ranges from 1:1 to 100:70.The reaction products or copolymers of the present invention arepositively charged (cationic) in the acid copper electroplatingcompositions of the present invention.

In general, the reaction products have a number average molecular weight(Mn) of 200 to 100,000, preferably from 300 to 50,000, more preferablyfrom 500 to 30,000, although reaction products having other Mn valuescan be used. Such reaction products can have a weight average molecularweight (Mw) value in the range of 1000 to 50.000, preferably from 5000to 30,000, although other Mw values can be used.

The amount of the reaction product included in the copper electroplatingbaths for plating copper metal of the present invention can range from 2ppm to 15 ppm, preferably, from 2 ppm to 10 ppm, more preferably, from 2ppm to 5 ppm, most preferably from 3 ppm to 4 ppm based on the totalweight of the plating bath.

Copper ion sources are copper salts (preferably water soluble) andinclude without limitation: copper sulfate, such as copper sulfatepentahydrate; copper halides such as copper chloride; copper acetate;copper nitrate; copper tetrafluoroborate; copper alkylsulfonates; copperaryl sulfonates; copper sulfamate: copper perchlorate and coppergluconate. Exemplary copper alkane sulfonates include copper(CI-C6)alkane sulfonate and more preferably copper (C₁-C₃) akanesulfonate. Preferred copper alkane sulfonates are coppermethanesulfonate, copper ethanesulfonate and copper propanesulfonate.Exemplary copper arylsulfonates include, without limitation, copperbenzenesulfonate and copper p-toluenesulfonate. Mixtures of copper ionsources may be used. Preferably, the copper salt is present in an amountsufficient to provide an amount of copper ions of 30 to 60 g/L ofplating solution. More preferably, the amount of copper ions is from 35to 50 g/L; most preferably, the amount of copper ions is from 35 to 45g/L.

The electrolyte of the present invention is acidic. Preferably, the pHof the electrolyte is less than or equal to 2; more preferably, the pHis less than or equal to 1. Acidic electrolytes include, but are notlimited to, sulfuric acid, acetic acid, fluoroboric acid, alkanesulfonicacids such as methanesulfonic acid, ethanesulfonic acid, propanesulfonicacid and trifluoromethane sulfonic acid, aryl sulfonic acids such asbenzenesulfonic acid, p-toluenesulfonic acid, sulfamic acid,hydrochloric acid, hydrobromic acid, perchloric acid, nitric acid,chromic acid and phosphoric acid. Mixtures of acids can be used in thecopper electroplating compositions of the present. Preferred acidsinclude sulfuric acid, methanesulfonic acid, ethanesulfonic acid,propanesulfonic acid, hydrochloric acid and mixtures thereof. Sulfuricacid is a most preferred acid. The acids can be present in amounts of 1to 400 g/L; preferably from 10 g/L to 300 g/L: more preferably from 25g/L to 250 g/L; most preferably from 30 g/L to 100 g/L. When sulfuricacid is included in the copper electroplating composition, a preferredconcentration range is 40 g/L to 80 g/L, most preferably, from 40 g/L to60 g/L. Electrolytes are generally commercially available from a varietyof sources and can be used without further purification.

Such electrolytes can, optionally, but preferably, contain a source ofhalide ions. Preferably, chloride ions and bromide ions are used.Exemplary chloride ion sources include copper chloride, sodium chloride,potassium chloride and hydrochloric acid. Examples of sources of bromideions are bromine chloride and bromine water. A wide range of halide ionconcentrations may be used in the present invention. Preferably, thehalide ion concentration is in a range of 0.5 ppm to 100 ppm based onthe plating bath. More preferably, halide ions are included in amountsof 50 ppm to 80 ppm, most preferably from 65 ppm to 75 ppm. Such halideion sources are generally commercially available and may be used withoutfurther purification.

The aqueous acid copper electroplating baths contain an accelerator.Accelerators (also referred to as brightening agents) include, but arenot limited to, N,N-dimethyl-dithiocarbamic acid-(3-sulfopropyl) ester;3-mercapto-propylsulfonic acid-(3-sulfopropyl)ester;3-mercapto-propylsulfonic acid sodium salt; carbonicacid,dithio-O-ethylester-S-ester with 3-mercapto-1-propane sulfonic acidpotassium salt; bis-sulfopropyl disulfide; bis-(sodiumsulfopropyl)-disulfide; 3-(benzothiazolyl-S-thio)propyl sulfonic acidsodium salt; pyridinium propyl sulfobetaine;1-sodium-3-mercaptopropane-1-sulfonate; N,N-dimethyl-dithiocarbamicacid-(3-sulfoethyl)ester; 3-mercapto-ethyl propylsulfonicacid-(3-sulfoethyl)ester; 3-mercapto-acid sodium salt; carbonicacid-dithio-O-ethylester-S-ester with 3-mercapto-1-ethane sulfonic acidpotassium salt; bis-sulfoethyl disulfide; 3-(benzothiazolyl-S-thio)ethylsulfonic acid sodium salt; pyridinium ethyl sulfobetaine; and1-sodium-3-mercaptoethane-1-sulfonate. A preferred accelerator of thepresent invention is N,N-dimethyl-dithiocarbamic acid-(3-sulfopropyl)ester. Preferably, accelerators are included in amounts of 0.1 ppm to1000 ppm. More preferably, the accelerators are included in amounts of10 ppm to 50 ppm, most preferably, from 40 ppm to 50 ppm.

Suppressors include, but are not limited to, polypropylene glycolcopolymers and polyethylene glycol copolymers, including ethyleneoxide-propylene oxide (“EO/PO”) copolymers and butyl alcohol-ethyleneoxide-propylene oxide copolymers. The weight average molecular weight ofthe suppressors can range from 800-15000, preferably 900-12,000.Preferably, suppressors are present at a range of 0.5 g/L to 15 g/Lbased on the weight of the composition; more preferably, from 1 g/L to 5g/L.

The electroplating baths can be prepared by combining the components inany order. It is preferred that the inorganic components such as sourceof copper ions, water, electrolyte and optional halide ion source arefirst added to the bath vessel, followed by the organic components suchas reaction product (leveler), accelerator, suppressor, and any otheroptional organic components.

The aqueous copper electroplating baths of the present invention can,optionally, contain a conventional leveling agent provided such theleveling agent does not substantially compromise the structure andfunction of the copper features. Such leveling agents may include thosedisclosed in U.S. Pat. No. 6,610,192 to Step et al., 7,128,822 to Wanget al., U.S. Pat. No. 7,374,652 to Hayashi et al. and U.S. Pat. No.6,800,188 to Hagiwara et al. However, it is preferred that such levelingagents are excluded from the baths.

Electroplating is preferably done from 15-65 ° C.; more preferably,electroplating is from room temperature to 50 ° C.; even morepreferably, from room temperature to 40 ° C.; and, most preferably, fromroom temperature to 30 ° C., wherein room temperature is optimum.

Preferably, the copper electroplating baths of the present invention areagitated during plating. Agitation method include, but are not limitedto: air sparging, work piece agitation, and impingement. Preferablyagitation is done from 10 cm/second to 25 cm/second, more preferablyfrom 15 cm/second to 20 cm/second.

A substrate is electroplated by contacting the substrate with theplating bath by immersing the substrate in the bath or by spraying thesubstrate with the bath. The substrate functions as a cathode. Theplating bath contains an anode, which may be a soluble anode or aninsoluble anode. Potential is applied to the electrodes. Currentdensities preferably range from 2 ASD to 8 ASD; more preferably, from 4ASD to 8 ASD; and most preferably, from 5 ASD to 7 ASD (e.g., such as 5ASD to 6 ASD, or 5 ASD to 7ASD, or 6 ASD to 7ASD).

After the substrate is electroplated with copper from the aqueous basedacid copper electroplating composition of the present invention, thecopper along with the substrate is annealed to complete the method ofpreparing the copper metal of the present invention. Preferably, theannealing is done at 200° C. or greater; more preferably. from 200° C.to 260 ° C.; most preferably from 230° C. to 250° C. Preferably,annealing is done from 2 hours to 10 hours; more preferably, from 5hours to 8 hours; most preferably, from 5.5 hours to 6.5 hours.Preferably, annealing is done in an inert atmosphere, such as a gaseousN₂ atmosphere. The annealing processes does not substantially increasecopper grain size.

In addition to the properties described above, the copper metal of thepresent invention has good mechanical properties of tensile strength (atbreak) and elongation% (at break). Preferably, the tensile strength atbreak of the copper metal of the present invention is equal to orgreater than 330 MPa; more preferably, from 330 MPa to 360 MPa.Elongation% at break is greater than or equal to 20% (e.g. 20% to 25%);preferably, from 21% to 23%.

While the copper metal of the present invention and the method ofelectroplating copper metal of the present invention can be used forcopper metallizing various substrates, preferably, the copper metal ofthe present invention is electroplated by the method of the presentinvention in the formation of fine line copper RDLs used as a way toreroute conduction paths within chip packages, such as in chip packageswhere fine line RDL has an LIS less than or equal to 10 μm×10 μm:preferably, 5 μm×5 μm; more preferably, less than or equal to 2 μm×2 μm;most preferably, less than or equal to 1 μm×1 μm.

In addition to copper plating RDLs, the copper electroplating method ofthe present invention can be used to electroplate copper metal of thepresent invention on dielectric substrates and semiconductors with metalseed layers, such as copper seed layers. Dielectric materials include,but are not limited to, thermoplastic resins and thermosetting resins. Aparticularly preferred dielectric material is polyimide. Semiconductormaterials include, but are not limited to, silicon.

The copper metal electroplating method can be used to non-conformallyelectroplate copper metal of the present invention on surfaces of thesubstrates as well as in apertures, such as vias. Preferably, theapertures, including vias, have high aspect ratios of 2:1 or greater;more preferably from 4:1 or greater; even more preferably from 6:1 orgreater, such as 10:1 to 20:1.

Apertures, such as vias, preferably, have diameters of 0.5 μm to 200 μm,more preferably, from 1 μm to 50 μm. The depth of the apertures canrange, preferably, from 0.5 μm to 500 μm; more preferably, from 1 μm to100 μm.

The following examples are included to further illustrate the inventionbut are not intended to limit its scope.

EXAMPLE 1 Leveler

Glycerol diglycidyl ether (60 mmols) and 1H-imidazole (100 mmols) wereadded at room temperature to a round-bottom reaction flask set in aheating bath. Then 40 mL of DI water were added to the flask. Thetemperature of the heating bath was set to 98° C. The reaction mixturewas heated for 5 hours and left stirring at room temperature for another8 hours. The reaction product (reaction product 1) was used withoutpurification. The molar ratio of the moieties from the 1H-imidazole tothe molar ratio of the ether moieties was 100:63.

EXAMPLE 2 Leveler

Glycerol diglycidyl ether (30 mmols) and an imidazole compound mixture(30 mmols) of 1H-imidazole (25% by mole)+4-phenylimidazole (75% by mole)were added at room temperature to a round-bottom reaction flask set in aheating bath. Then 40 mL of DI water were added to the flask. Thetemperature of the heating bath was set to 98° C. The reaction mixturewas heated for 5 hours and left stirring at room temperature for another8 hours. The reaction product (reaction product 2) was used withoutpurification. The molar ratio of the moieties from the imidazole mixtureto the molar ratio of the ether moieties was 1:1.

EXAMPLE 3 Leveler

2-(2-aminoethyl)pyridine (100 mmols) was added at room temperature to around-bottom reaction flask set in a heating bath. Then 40 mL of DIwater were added to the flask. The temperature of the heating bath washeated to a jacket temperature set at 90° C. Once the bath reached aninternal temperature of 76-78° C., glycerol diglycidyl ether (100 mmols)was slowly fed into the round-bottom reaction flask to moderate anyexotherm. The reaction mixture was heated with the jacket temperatureset at 90° C. for 4 hours with stirring. The reaction mixture was thencooled down to 50-55° C. and a sulfuric acid solution was added todilute the mixture to 40 wt %. The final reaction product (reactionproduct 3) was cooled to 25° C. then gravity drained. Reaction product 3was used without purification. The molar ratio of the moieties from theimidazole mixture to the molar ratio of the ether moieties was 1:1.

EXAMPLE 4 Comparative Leveler

In a 250 mL round-bottom, three-neck flask equipped with a condenser anda thermometer, 100 mmol of 1H-imidazole and 12 mL DI water were addedfollowed by addition of 200 mmol of epichlorohydrine. The resultingmixture was heated for 5 hours using an oil bath set to 95 ° C. and thenleft to stir at room temperature for an additional 8 hours. The reactionproduct was transferred to a 200 mL volumetric flask, rinsed andadjusted with DI water to the 200 mL mark. The reaction product(comparative reaction product) solution was used without furtherpurification.

EXAMPLE 5 Copper Electroplating Baths of the Present Invention

The following aqueous copper electroplating baths were prepared at roomtemperature by mixing and stirring the components of the bath in water.

TABLE 1 COMPONENT BATH 1 BATH 2 BATH 3 Copper ions from 40 g/L 40 g/L 40g/L copper sulfate pentahydrate Aqueous based 50 g/L 50 g/L 50 g/LSulfuric acid (98 wt %) Chloride ions from 70 ppm 70 ppm 70 ppm aqueoushydrogen chloride (99 wt %) N,N-dimethyl- 50 ppm 50 ppm 50 ppmdithiocarbamic acid- (3-sulfopropyl) ester EO/PO random  5 g/L  5 g/L  5g/L copolymer with terminal hydroxyl groups (Mw around 1000) ReactionProduct 1  4 ppm — — leveler Reaction Product 2 —  4 ppm — levelerReaction product 3 — —  4 ppm leveler Water To one liter To one liter Toone liter The pH of the aqueous copper electroplating baths was lessthan 1.

EXAMPLE 6 Comparative Copper Electroplating Bath

The following aqueous copper electroplating bath was prepared at roomtemperature by mixing and stirring the components of the bath in water.

TABLE 2 COMPONENT COMPARATIVE BATH Copper ions from copper sulfatepentahydrate 50 g/L Aqueous based Sulfuric acid (98 wt %) 100 g/LChloride ions from aqueous hydrogen chloride 50 ppm (99 wt %)N,N-dimethyl-dithiocarbamic acid-(3- 10 ppm sulfopropyl) ester EO/POrandom copolymer with terminal 2.5 g/L hydroxyl groups (Mw around 1000)Comparative reaction product leveler from 10 ppm Example 4 Water To oneliter The pH of the aqueous copper electroplating bath was less than 1.

EXAMPLE 7 Copper Electroplating with Bath 1 of the Invention

A copper blank silicon wafer (size=4 cm×4 cm) with a copper seed layerof 1500 Å thick was placed into a plating cell which included theaqueous copper electroplating composition of Bath 1 from Example 5. ThepH of the bath during plating was less than 1 and the platingcomposition was paddle agitated with a linear speed of 20 cm/secondduring plating. A soluble copper electrode served as an anode. DCplating was done at room temperature using a current density of 6 ASD.Copper electroplating was done until a copper deposit having a thicknessof 20 μm was plated on the wafer. The copper deposit was annealed in aninert N₂ atmosphere filled oven at 230° C. for 6 hours. After annealing,the copper metal plated wafer was cooled to room temperature.

EXAMPLE 8 Copper Electroplating with the Comparative Bath

A copper blank silicon wafer (size=4 cm×4 cm) with a copper seed layerof 1500 Å thick was placed into a plating cell which included theaqueous copper electroplating composition of the comparative bath fromExample 6. The pH of the bath during plating was less than 1 and theplating composition was paddle agitated with a linear speed of 20cm/second during plating. A soluble copper electrode served as an anode.DC plating was done at room temperature using a current density of 6ASD. Copper electroplating was done until a copper deposit having athickness of 20 μm was plated on the wafer. The copper deposit wasannealed in an inert N₂ atmosphere filled oven at 230° C. for 6 hours.After annealing, the copper metal plated wafer was cooled to roomtemperature.

EXAMPLE 9 Analysis of Copper Electroplated Segments

EBSD was used to quantitatively measure properties of the copperdeposits from Examples 7 and 8. The EBSD revealed grain size, grainorientation, texture, and grain boundary angles.

4 mm×8 mm pieces of the plated copper wafer (300 mm polycrystallinesilicon, P/boron, <100>, 0-100 ohm-cm from Pure Wafer, 2240 RingwoodAve. San Jose Calif. 951311) was cut and mounted on a sample holder.Argon milling cross section polisher Model JEOL IB09010CP from JEOL USA,Inc. was used to polish the surface of each piece, and the surfaces wereanalyzed. FE-SEM (FEI model Helios G3) coupled with EBSD detector (EDAXInc., model Hikari Super and data was analyzed by OIM™ Analysissoftware) was used to collect diffracted signals from the samples. Forgrain size analysis. step size was 0.025 μm (measured at every 0.025 μmintervals) with 10 scans at different random sample locations werecollected to obtain statistically significant data. For textureanalysis, the step size is 0.075 μm (measured at every 0.075 μMintervals) with 5 different location scans (statistically significant).

FIGS. 1 and 2 show the EBSD Inverse Pole Figure (IPF) for the presentinvention and the comparative example, respectively, showing variousorientations as indicated by the different shades in the Figures. Inboth FIGS. 1 and 2, the bold dark outlines indicate twin fractions ofadjacent grain boundaries at the <111> direction with misorientationangles of 60°±5° as indicated by the arrows in each Figure. Adjacentgrain boundaries which have misorientation angles which fall outside therange of 60°±5° are shown by the thin, non-bold lines. In FIG. 1, themisorientation angles which fall outside the scope of the 60°±5° are 5°,40° and 93°. With respect to FIG. 1, misorientation angles of 60°±5°make up 35% with the remainder of misorientations outside this range. InFIG. 2, the misorientation angles which fall outside the scope of the60°+5° are 23°, 39° and 139°. With respect to FIG. 2, misorientationangles of 60°±5° make up only 15% with the remainder of misorientationsoutside this range. The comparative copper metal of FIG. 2 hasmisorientation angles of 60°±5° of less than half the number of thecopper metal of the present invention of FIG. 1.

EBSD was used to determine misorientations between two adjacent grainsas shown in FIGS. 1 and 2.

Copper wafers from Examples 7 and 8 were mechanically broken toapproximately 1 cm×2 cm pieces. Each piece was then mounted with copperfacing up on a plastic sample holder using double-sided tape. A BrukerD8 Advance θ-θ X-ray diffractometer (XRD) equipped with a coppersealed-source tube and Vantec-1 linear position sensitive detector wasused to collect diffraction patterns (Bruker AXS Inc. 5465 East CherylParkway, Madison Wis. 53711). The tube was operated at 35 kV and 45 mAand the samples were illuminated with copper Kα radiation (1=1.541 Å).XRD data were collected with a 3° detector window from 15° to 84°2θ,with a step size of 0.0256° and 1 s/step collection time. Analysis wasperformed with Jade 2010 MDI software application available from KSAAnalytical Systems, Aubrey, Tex.

Mechanical Property Tests were performed using INSTRON™ Pull Tester33RR64. Test specimens were first plated on a stainless steel substrates(dimensions 12 cm×12 cm) using the formulations in Examples 7 and 8under the same plating conditions and plated at a current density of6ASD. The plated copper was then peeled off the stainless steel platesand cut to strips with dimension of 1.3 cm×10 cm. The thickness of thestandalone copper films was 50 μm. The test procedure (IPC-TM-650) wasfollowed in this test using an INSTRON™ pull tester 33R4465. The copperstrips were annealed in a furnace (Blue M industrial laboratory ovenModel 01440A) at 230° C. for 6 hours. After allowing the samples to coolto room temperature, the samples were tested in the pull tester. Thepull rate applied was 0.002 inches/minute until the samples broke. Thedata was recorded with Bluehill-3 software, available from INSTRON®.Table 3 shows the results of the elongation test. The mechanical pulltest showed that the sample of the present invention had improvedtensile strength vs. the comparative sample while not sacrificingsignificant elongation performance.

Table 3 shows the comparisons of the copper deposits of the inventionvs. the comparative or conventional bath. The grain size for the copperdeposits of the present invention were approximately 43% less than thecopper from the comparative example after thermal annealing.

The EBSD was also used to determine the twin fraction and the textureindex for the copper deposits of the present invention and thecomparative copper. The copper deposits of the present invention showedtwin fractions of 35% of grain boundaries with 60°±5° misorientationsbetween adjacent grains at a crystal plane direction of <111>. Thetexture index for the copper metal of the present invention was 5.7 at(111) plane orientation. High (111) plane orientation is preferred asthe slip system for copper is {111}<110>. High (111) plane fraction canfacilitate the slip to occur easily which results in better mechanicalperformances. On the other hand, in the comparative copper metal, (001)plane orientation texture dominated with a texture index ratio of 5.1,which is not favorable for the system to slip. The (111) plane and the(001) plane are the two most significant planes in terms or MRD>2 incopper. Therefore, the two planes were compared where the higher numberof (111) planes vs. (001) planes was preferred for the copper metal ofthe invention.

XRD also revealed that the copper metal of the present invention hadsignificantly higher (111)/(200) ratio than that of the comparativecopper metal. Samples for the XRD test were about 5 μm thick copper filmplated by the copper baths of Examples 7 and 8 on silicon wafers. Theratio was determined using diffraction peak at (200) plane orientationbecause the (200) plane orientation was the second strongest diffractionpeak after (111). Other diffraction peaks were too weak or were unableto be detected. Diffraction intensity (I) vs. diffraction angle 2θ (°)was recorded and plotted for each sample as shown in FIG. 3. The areaunder the specific diffraction peak (111) orientation and diffractionpeak (200) orientation, was integrated for further quantification.Integration was done by Jade 2010 MDI software for XRD systems. Theresults are shown in Table 3.

TABLE 3 Performance Comparison Bath 1 Comparative Analysis MethodParameters (Invention) Example EBSD Grain size (μm), 2.3 4 sphericalequivalent diameter Twin fraction by 35% 15% length (μm/μm) Texture(111) 5.7 2.3 Texture (001) 1.3 5.1 XRD (111)/(200) 5.36 3.68 Area RatioMechanical Pull Tensile Strength (at 350 290 Test break) (MPa)Elongation % (at 23% 25% break)

EXAMPLE 10 Analysis of Copper Electroplated Segments from Bath 2 of theInvention

Copper metal was plated from Bath 2 on the same type of substrate asdisclosed in Example 7 above. The plating conditions were substantiallythe same as disclosed in Example 7. Copper plated from the copperelectroplating composition of Bath 2 disclosed in Table 2 in Example 5was analyzed for its properties according to the methods described inExample 9 above. The results of the EBSD, XRD and mechanical pull testresults are disclosed in Table 4 below.

TABLE 4 Analysis Method Parameter Bath 2 (Invention) EBSD Grain size(μm), spherical 1.9 equivalent diameter Twin fraction by length 52%(μm/μm) Texture (111) 10.2 Texture (001) 1.8 XRD (111)/(200) Area Ratio31 Mechanical Pull Test Tensile Strength (at break) 360 (MPa) Elongation% (at break) 21%

EXAMPLE 11 Analysis of Copper Electroplated Segments from Bath 3 of theInvention

Copper metal plated from Bath 3 was plated on the same type of substrateas disclosed in Example 7. Plating conditions were substantially thesame as in Example 7. Copper plated from the composition of Bath 3disclosed in Table 2 in Example 5 was analyzed for its propertiesaccording to the methods described in Example 9 above. The results ofthe EBSD, XRD and mechanical pull test results are disclosed in Table 5below.

TABLE 5 Analysis Method Parameter Bath 3 (Invention) EBSD Grain size(μm), spherical 1.4 equivalent diameter Twin fraction by length 35%(μm/μm) Texture (111) 8.4 Texture (001) 3.5 XRD (111)/(200) Area Ratio21 Mechanical Pull Test Tensile Strength (at break) 330 (MPa) Elongation% (at break) 23%

What is claimed is:
 1. A copper metal comprising twin fractions of 30%or greater of grain boundaries between adjacent copper grains havingangles of misorientation from 55° to 65° with respect to a crystal planedirection of <111>.
 2. The copper metal of claim 1, further comprisingan XRD area ratio of (111) plane orientation/(200) plane orientation atdiffraction angle 2θ (°) is equal to or greater than
 1. 3. The coppermetal of claim
 2. wherein the XRD area ratio of (111) planeorientation/(200) plane orientation at the diffraction angle 2θ (°) isequal to or greater than
 5. 4. The copper metal of claim 1, wherein acopper grain diameter is 100 nm or greater after thermal annealing.
 5. Amethod of electroplating copper comprising: a) providing a substrate; b)providing a copper electroplating bath comprising one or more sources ofcopper ions to provide the copper ions at concentrations of 20 g/L to 55g/L, one or more reaction products of one or more imidazole compounds,or one or more 2-aminopyridine compounds with one or more bisepoxides,wherein the one or more reaction products are at concentrations of 2 ppmto 15 ppm; an electrolyte; one or more accelerators, wherein the one ormore accelerators are at concentrations of 0.5 ppm to 100 ppm; and oneor more suppressors, wherein the one or more suppressors are atconcentrations of 0.5 g/L to 10 g/L; c) immersing the substrate in thecopper electroplating bath; d) electroplating copper on the substrate todeposit a copper layer on the substrate; and, e) annealing the copperlayer to a temperature of at least 200 ° C. in an inert atmosphere toprovide a copper layer comprising twin fractions of 30% or greater ofgrain boundaries between adjacent copper grains having angles ofmisorientation of 55° to 65° with respect to a crystal plane directionof <111>.
 6. The method of claim 5, wherein a current density duringelectroplating the copper is 2-8 ASD.
 7. The method of claim 5, whereinthe substrate comprises a dielectric with a metal seed layer adjacentthe dielectric, and wherein the copper layer is deposited adjacent themetal seed layer of the dielectric.